Gray pixels along a line's edge are almost always anti-aliasing (the smoothing most drawing and export tools apply automatically) or JPEG compression halos, not a resolution problem. A commercial press reproduces those in-between gray values (an 8-bit file allows 254 shades between black and white) as a pattern of small dots rather than solid ink, which makes a line that looked crisp on screen print soft or fuzzy — something reviewers can flag as "low resolution" even when the file is genuinely 300 DPI.
Two different problems that look similar
| Problem | Cause | Fix |
|---|---|---|
| Too few pixels for the print size | File generated or exported smaller than the page needs at 300 DPI | Generate at the target pixel size (see the DPI guide) |
| Gray, soft-edged lines at full resolution | Anti-aliasing and/or JPEG compression softening edges | Convert to solid black-and-white (1-bit), not just resize |
A file can be exactly 300 DPI and still look muddy in print, because DPI measures pixel density, not whether each pixel is pure black, pure white, or something gray in between.
What anti-aliasing actually does
Most drawing tools and image exporters smooth jagged diagonal and curved edges by blending edge pixels toward the background color — a black line on white gets a thin rim of gray pixels where it curves. On a screen, that smoothing makes edges look cleaner. On a printing press, which reproduces color and gray tones as patterns of small dots (halftone screening) rather than continuous shading, those gray edge pixels become a fine dot pattern instead of a solid line edge, and the eye reads that pattern as blur or softness rather than a crisp line.
What JPEG compression adds on top
JPEG compression works by discarding detail it judges visually unimportant, and it does this most aggressively right at sharp edges — exactly where a coloring page's black line meets white paper. The result is a halo of gray or off-color pixels hugging every line, on top of whatever anti-aliasing was already there. Two rounds of JPEG compression (export, then re-save) compound the effect. Files kept as PNG until the final export avoid this second source of gray edge pixels, though PNG alone doesn't remove anti-aliasing from the original artwork.
Why KDP's own guidance points here
KDP's image formatting guidance describes pixelation as covering blurry, grainy, or out-of-focus results generally, and notes explicitly that a file can carry a 300 DPI tag and still look blurry — attributing that to an altered DPI tag or an out-of-focus source image. Gray anti-aliased or compression-softened edges are a version of the same visible symptom: the file passes a DPI-only check but still doesn't read as a clean printed line, because the underlying pixels along every edge aren't solid black or solid white.
The fix, not just the diagnosis
Resolution and dithering are separate axes; a file needs to be right on both. Regenerating at a higher pixel size fixes low DPI but does nothing for gray edges that were already there. The fix for gray edges is thresholding the image down to exactly two values — pure black, pure white — which removes anti-aliasing and compression halos in the same step (see the 1-bit vs. grayscale guide for why this has to be the last step — after any resizing, never before it).
Sources
Last verified 2026-09-04. Updated 2026-09-04.